Remove stdlib.h #include added in r319844

A previous iteration of the tests I added in r319844 involved free(3), but
that attempt didn't pan out, so I switched to stack allocated buffers instead
of heap allocated ones, making the #include unnecessary.

MFC after:	1 month
MFC with:	r319844

lib/libcam/tests/libcam_test.c

@@ -30,7 +30,6 @@ __FBSDID("$FreeBSD$");
 #include <errno.h>
 #include <fcntl.h>
 #include <stdio.h>
-#include <stdlib.h>
 #include <camlib.h>
 
 #include <atf-c.h>